In ancient annals we find this tradition about the Sibylline Books. An old woman, a perfect stranger, came to king Tarquin the Proud, bringing nine books; she declared that they were oracles of the gods and that she wished to sell them. Tarquin inquired the price; the woman demanded an immense and exorbitant sum: the king laughed her to scorn, believing her to be in her dotage. Then she placed a lighted brazier before him, burned three of the books to ashes, and asked whether he would buy the remaining six at the same price. But at this Tarquin laughed all the more and said that there was now no doubt that the old woman was crazy. Upon that the woman at once burned up three more books and again calmly made the same request, that he would buy the remaining three at the original figure. Tarquin now became serious and more thoughtful, and realising that such persistence and confidence were not to be treated lightly, he bought the three books that were left at as high a price as had been asked for all nine. Now it is a fact that after then leaving Tarquin, that woman was never seen again anywhere. The three books were deposited in a shrine and called “Sibylline”; to them the Fifteen resort whenever the immortal gods are to be consulted as to the welfare of the State.

— Gellius

Confidence and persistence have been used as destructive tools — weapons, I guess— as long as modern humans existed. Was the woman insane, or just a very confident huckster? One thing we know for certain is that those books were not oracles, so she must have been one or the other. It may be that insanity and supreme confidence are the same thing. The world is the way it is because people can be manipulated by confidence, and almost nobody is immune to unflinching confidence over a long enough period.